Advanced apparatus and method for abatement of gaseous pollutants

ABSTRACT

An apparatus and method are provided for treating pollutants in a gaseous stream. The apparatus comprises tubular inlets for mixing a gas stream with other oxidative and inert gases for mixture within a reaction chamber. The reaction chamber is heated by heating elements and has orifices through which cool or heated air enters into the central reaction chamber. A process is also provided whereby additional gases are added to the gaseous stream preferably within the temperature range of 650 C.-950 C. which minimizes or alleviates the production of NOx.

[0001] The present invention relates to an apparatus and method for thetreatment of gas streams containing organic and inorganic pollutants,suitable for applications such as treatment of streams resulting fromfabrication of semiconductor materials and devices, micro-electricproducts, manufacturing of compact discs and other memory devices.

BACKGROUND OF THE INVENTION

[0002] The gaseous effluents from the manufacturing of semiconductormaterials, devices, products and memory articles involves a wide varietyof chemical compounds used and produced in the process facility. Theycontain inorganic and organic compounds, breakdown products ofphoto-resist and other reagents, and a wide variety of other gases whichmust be removed from the waste gas streams before being vented from saidfacility. Typical to the industry, such effluents, either as a singlecomponent or multi-component composition, are mixed with an oxidant,such as high purity oxygen, air, nitrous oxide, or other reagents andthermally reacted and/or oxidized at elevated temperatures in a centralreaction chamber.

[0003] In semiconductor manufacturing processes, various processingoperations can produce combustible gas streams. Hydrogen and a varietyof hydrides, VOC's, PFC's, HAP's, etc. may be present and, if combinedwith air, oxygen or other oxidant species such as nitrous oxide,chlorine, fluorine and the like, form reactive mixtures.

[0004] However, the composition of the waste gas generated at aworkstation may vary widely over time as the successive process stepsare carried out. Additionally there are many different wafer processtools with many different recipe chemistries used in typicalsemiconductor process facilities.

[0005] With this variation of the composition of waste gas streams andthe need to adequately treat the waste gas on a continuous basis duringthe operation of the facility, a common approach taken is to provide asingle large-scale waste treatment system for an entire processfacility. Such systems are almost always over-designed in terms of itstreatment capacity, and typically do not have the ability to safely dealwith a large number of mixed chemistry streams without posing complexreactive chemical risks. The operating cost associated with heating anextremely dilute mixed gas stream to appropriate elevated temperaturesto achieve abatement performance targets is also an issue, in additionto the huge capital cost associated with large scale oxidation units,which often use catalytic chemistry. Furthermore, one of the problems ofgreat concern in gas effluents is the formation of acid mist, acidvapors, acid gases and NOx (NO, NO₂). The present invention provides amethod for alleviating the formation of NOx by the appropriate injectionof additives into the reactor which not only minimizes or eliminates NOxformation, but also yield less acidic, hence less corrosive effluents.

[0006] The present invention provides compact, dedicated units, whichmay be employed at the point of use. They are designed to serve a singletool, or group of similar chemistry process tools, individual processingoperation, or group of abatement compatible process operations toeffectively and efficiently remove pollutants without beingover-designed with respect to volume capacity, chemical complexity, heatgeneration and power consumption.

SUMMARY OF THE INVENTION

[0007] The present invention provides a process for abating chemicalpollutants in a pollutant-containing gas stream by introducing the gasstream into a reactor chamber through a conduit, which accommodates atleast one secondary inlet through which is introduced at least onegaseous reagent (with or without additional gaseous, liquid or solidreagents) to cause a controlled reaction in the gas stream by mixing andoptionally, by heating. The desired reagent may also be generated insitu (e.g., thermally formed) in the mixing stream. Said reagent(s),added through inlets and/or directly or as precursor(s) into the reactorchamber, may be selected from the group consisting of hydrogen,hydrocarbons, ammonia, air, oxygen, water vapor, alcohol, ethers,calcium compounds, amines, and a mixture of these gases, liquids and/orsolids. For example, mixtures such as ammonia/air and ammonia/oxygenhave been found to be useful reagents. The reaction of the pollutantcontaining gas stream with the reagent is within the temperature rangeof about 650 C. to 950 C.

[0008] The present invention provides an apparatus for removingpollutants from gaseous streams. It comprises a pre-reaction injectionsection, a thermal reactor section and a liquid scrubber section toachieve target abatement performance. In one embodiment, ports arelocated in the pre-reactor injection section and/or the main thermalreaction chamber for introducing a gas in such a way as to reduce oralleviate particle build-up in the main reactor section.

[0009] The thermal reactor is provided with at least one inletcomprising a conduit terminating with a portion of the conduit withinthe reactor which projects into the reactor into a tube defining an areain which there could be flame formation (hot zone or reaction zone).

[0010] The thermal reactor comprises a central chamber accommodatingheating elements, a side inlet communicating with an exterior air spacebetween the exterior wall and the heating elements, and an interior airspace optionally communicating with the exterior air space. There isalso, optionally, a distributor for introducing a gas, liquid and/orsolid into the central chamber at a distance from the open end of thetube.

[0011] In one embodiment, the distributor is located out of the hotzone. The interior air space is defined by the interior wall and theheating elements, and an orifice means of introducing gas, liquid and/orsolid into the central chamber through the interior wall, the inletsection, and/or the central chamber open end. The orifice may be locatedupstream of a hot zone created at the open end of the conduit and/orlocated downstream of the hot zone. The gases exiting the thermalreactor are cooled when passed through a liquid cooling sectioncontaining a vortex and/or spray chamber.

[0012] The cooled gases from the combustion chamber are then passedthrough a counter-current and/or co-current flow packed bed liquidscrubber for chemical pollutant scrubbing and trapping and condensingparticles by flowing the gas stream through the packed bed with oragainst a flowing liquid. Inlets are provided for introducing gases tothe upper portion of the bed to lower the exhaust dew point.

[0013] The present invention also, optionally, has a means of sensinggases, liquids and/or solids for the purpose of monitoring and/orcontrolling the invention at desired and/or optimal operatingconditions.

BRIEF DESCRIPTION OF THE DRAWING

[0014]FIG. 1 is a diagram of an intake conduit according to the presentinvention illustrating a chamber for the introduction of gas along thewall of the chamber and an optional gas distributor.

[0015]FIG. 2 is a cut-away view of the elevation of a thermal reactoraccording to the present invention.

[0016]FIG. 3 is a cut away view of a liquid vortex design according tothe present invention.

[0017]FIG. 3a is a cut away view of another example of a liquid vortexdesign according to the present invention.

[0018]FIG. 4 is a diagram of an apparatus comprising the thermal reactorand packed bed liquid scrubber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Referring to FIG. 1, there is shown the entry end of a reactionchamber 10 wherein the process gases are introduced through, optionally,one or more inlets 11 of the pre-reaction chamber section. The lowerportion of inlet 11 is surrounded by annular chambers 12 into whichreagent gas liquid and/or solid, air or oxygen is introduced throughport 13 and which exit into the reaction chamber through outer port 14at the exit of inlet 11. Another annular chamber 15 is provided forintroducing nitrogen or other gas, which enters chamber 15 through port16 and which exits the circumferential port 17 to flow the gasdownwardly along the inside surface of the reactor wall 18 (or otherstrategical injection point). The flow of the gas along the reactor wallreduces or alleviates the build-up of particulate matter.

[0020] In some instances, a hot zone or reaction zone is created at theexit of inlets 11 within the reaction chamber and it may be desirable ornecessary to introduce other reagent(s). For this purpose, a gas, liquidand/or solid distributor 19 is optionally provided downstream of theinlets 11 and within or outside of said reaction or hot zone.

[0021] A preferred embodiment of the use of apparatus according to thepresent invention is for abating a chemical pollutant-containing gasstream by a controlled mixing of said gas stream with one or morereagent(s), preceding and/or followed by flowing this mixture throughthe main reaction chamber maintained under controlled conditions, toeffect desirable reaction(s) during this passage. Particularly preferredreagents are hydrogen, hydrocarbons, ammonia, air, oxygen, water vapor,alcohol, ethers, calcium compounds and amines. The alcohols are loweralcohols such as methanol, ethanol, and the like. Ethers are lowerethers such as dimethyl ether, methyl ethyl ether, and the like. Theamines are lower amines such as methylamine, dimethyl amine, and thelike. A particularly preferred mixture is a combination of ammonia andoxygen or air. This mixture is particularly preferred for streamscontaining halogens, such as chlorine and/or fluorine. Thus ammonia,ammonia and air, or ammonia and oxygen are added under controlledconditions to the process gas in a mixing zone of the reaction chamberwithin the temperature range of about 650 C.-950 C. A particularadvantage of this process is that the pH of the liquid from the scrubberis raised to approximately 3-10, which creates a much less corrosiveenvironment than the more acidic liquids and vapors typically formed.

[0022] Oxygen or other gases, liquids and/or solids may be addeddownstream of the mixing zone to obtain optimal performance on start-up,the mixture and/or temperature can then be readjusted during thecleaning cycle. As shown in FIG. 1, the downstream introduction of gasesmay be through a tube 19 for directing gas downstream, or may be anothergas distributing device such as a manifold or injector.

[0023] Referring to FIG. 2, there is shown a thermal reactor accordingto the present invention. Process gas enters through inlets (not shown)at the top of the reactor into the central chamber 40. Heating elements41 a are electrically heated to provide high temperature hot surfaces onthe interior wall 42. Heating elements 41 a are shown as annularlylocated surrounding the chamber 40. Optionally, heating elements 41 bmay also be located within chamber 40. Air (cool or heated) may beintroduced into the reactor chamber 40 anywhere at the inlet end and/orexit end of chamber 40 or somewhere in between by ways of single and/ormultiple injection points, not shown.

[0024] The location of the injection points may be varied according tothe desired configuration of the reactor. For example, there istypically a hot zone created at the entry end of the reactor where theprocess gas and reagents are introduced. Depending upon the optimumchemistry and stoichiometry, the injection points may be locatedupstream, in or downstream of the hot zone.

[0025] Referring to FIG.3, there is shown a liquid vortex 50. The gasesexit the reactor at the bottom of chamber 40 into a liquid vortex 50,where liquid enters through 51 tangentially into outer chamber 52 tocreate a swirling motion, causing the liquid to rise and overflowinternal wall 53 into the main chamber 54 to control the temperature ofthe surface and to maintain a continuous liquid film on the wall. This,along with additional liquid sprays, allows contact between the liquidand gases, liquids and/or solids to cool down the gaseous stream totemperatures typically below 100° C. The liquid vortex optionally mayhave an insert (not shown) extending the reactor chamber 40 to any pointinto the vortex.

[0026] A modification is shown in FIG. 3A where the liquid entersdirectly into the gas stream through nozzle 51A.

[0027] The gases then exit the liquid vortex section cooled to less than100° C.

[0028] Referring now to FIG. 4, there is shown in diagram form aprocessing facility using all of the above-described features. Theprocess gas from one or more stations enters the inlets 70, and ismixed, if required, with a reagent gas, liquid and/or solid, oxygen orother gas and with an inert purge gas, such as nitrogen as described inconnection with FIG. 1. The capacity of the facility will depend uponthe size of hardware components, types of process gases and reagents,etc. Typical gas flow rates through the facility are less than about 300slm. The gases are then treated in the thermal reactor 74, to which airis optionally introduced through lines 72 and/or 75. The gases exitingthe bottom of thermal reactor 74 pass through a vortex 76 of liquidflowing through line 77 (plus optionally a water spray 78) into thepacked bed liquid scrubber 60. The gases from the thermal reactor exitthrough conduit 61 and pass through a water spray and into a packed bedcontaining packing 63 through which the gases are flowed incounter-current and/or optionally co-current manner through the packingwith and/or against the flow of water provided by continuous sprayer 64.Particle-containing liquid flows to the bottom to exit to a sump tank,and/or recirculation tank, and/or direct drain. The gas is typicallydirected via ports 61A to a demister section 65 where moisture andadditional particulate are removed via demister packing 66 and thecleaning of this section is accomplished with liquid provided by acontinuous and/or an intermittent sprayer 67. Air is injected throughport 68 to provide direct gas cooling and promote reduction of the dewpoint of the exiting gas. The treated gas then exits through flue 69.

[0029] Optional detectors can be located in the invention to monitortarget components. Such information is then fed back to control theabatement parameters, such as temperature and feed rate of individualreagents etc.

EXAMPLE 1

[0030] In an apparatus as shown in FIG. 4 with inlets as shown in FIG.1, F₂ (fluorine) a by-product present in semiconductor process gases wastested. The abatement achieved (measured as % DRE, decomposition removalefficiency) and NOx formation, based on 20% utilization of the F₂ weremeasured. The optimum gas flow rate (in standard liters/min, slm) andAmmonia gas addition at the reactor inlet are given to achieve theindicated DRE. Pump NH3 flow, purge, Test # Gas Flow, SLM SLM SLM % DRENO out, PPM NO2 out, PPM 2 F2 1.0 to 4.0 3.0  50 99.9+ <30 LDL* <30 LDL1 F2 1.0 to 2.0 1.0 to 3.0 100 99.9+ <40 LDL  <40 LDL

[0031] Test 1—A constant flow of 3.0 SLM of NH3 was used to treatincreasing flows of F2 (1.0 to 4.0 SLM). DRE remained above 99.9% forthe range of testing. F2 DRE was consistently above 99% for the widestrange of flows.

[0032] Test 2—F2 was tested at 1.0 and 2.0 SLM as NH3 was varied from1.0 to 3.0 SLM. Again, DRE remained above 99.9%.

[0033] LDL is the calculated Lower Detection Limit for the QuadripoleMass Spectrometer at the settings used in the R&D lab. NO and NO2typically did not register in any of the QMS readouts.

EXAMPLE 2

[0034] In a similar device, Cl₂ (chlorine) a by-product present insemiconductor process gases was tested. The abatement achieved (measuredas % DRE, decomposition removal efficiency) and NOx formation, based on20% utilization of the Cl2 were measured. The optimum gas flow rate (instandard liters/min, slm) and Ammonia gas (NH3) addition at the reactorinlet are given to achieve the indicated DRE. Pump NH3 flow, purge, Test# Gas Flow, SLM SLM SLM % DRE NO out, PPM NO2 out, PPM 1 Cl2 1.0 1.0 to6.0 240 96+  <40 LDL <40 LDL 2 Cl2 0.25 to 1.5 1.5 100 94+  <40** <10 1Cl2 1.5 3.0 100 99.0 <40 <10

[0035]

[0036] Test 1—Cl2 was held constant at 1.0 SLM as NH3 was varied from1.0 to 6.0 SLM. The DRE remained above 96% and climbed as high as 99.9%at higher NH3 flows.

[0037] Test 2—NH3 was held constant at 1.5 SLM as Cl2 flow was changedfrom 0.25 to 1.5 SLM. DRE varied from 99.99% for the 0.25 SLM Cl2 flowto 94% for the 1.50 SLM Cl2 flow.

[0038] Test 3—NH3 was raised from 1.5 to 3.0 SLM with the Cl2 fixed at1.5 SLM. This test was performed to compare DRE as a function of moleratio of NH3 to Cl2. The higher flows had a greater DRE than the lowerflows at the same mole ratio.

EXAMPLE 3—NF3

[0039] In a similar device to that described in example 1, nitrogentrifluoride (NF3) was tested for abatement efficiency and nitric oxideand/or nitrogen dioxide (NOx) formation. Abatement efficiencies ≧99.999%were achieved for all influent NF3 flows tested (0.125-0.5 standardliters per minute (sim)) with a minimum hydrogen inlet concentration* of10%. At hydrogen inlet concentrations ≧18%, NOx formation was suppressedto below the analytical instrumentation's detection limit.

EXAMPLE 4—NOx

[0040] In another similar device, testing was performed to determine thecapability of the system for NOx abatement. 100 standard cubiccentimeters per minute (sccm) of NOx was injected into the abatementdevice inlet. Test variables included thermal reactor set-points of 700C. and 850C. and hydrogen inlet concentrations between 5 and 18 sim.Abatement efficiencies of >70 and >85% were achieved at 700 C. and 850C., respectively, with a hydrogen inlet concentration of 18%.

EXAMPLE 5

[0041] In a device similar to that described in Example 1, using argonas a process gas flowed at 35 slm at temperatures varying from about 700C. to 840 C., oxygen and/or ammonia were added to the flow stream.Oxygen was added using 5 or 8 slm. Ammonia was added at incrementsbetween 0.25-6.0 slm. The temperature at the point which the gases aremixed was held constant at 850 C. The product stream was analyzed bymass spectrometry, particularly for oxygen, nitrogen, NOx and ammonia.It was found that when using a combination of oxygen and ammonia, asammonia was increased, holding oxygen constant, initially NOx formationincreased with ammonia concentration. Beyond a threshold, the NOxconcentration decreased. This indicates an operating condition whereoptimal ammonia and oxygen flow rates where the chemistry andstoichiometry favor a reduction of NOx.

[0042] The invention having been fully described, further modificationsof the invention will become apparent to those of ordinary skill in theart. Such modifications are within the scope of the invention, which isdefined by the claims set forth below.

What is claimed is:
 1. A process for abating chemical pollutants in apollutant-containing gas stream comprising the steps of introducing saidgas stream into a reaction chamber through a pre-reaction sectioncomprising at least one conduit accommodating at least one secondaryinlet for introducing additional gases, liquids and/or solids into saidpre-reaction section; introducing at least one additional gas, liquidand/or solid into said secondary inlet; a causing a reaction of said gasstream with said additional gas, liquid and/or solid by mixing and,optionally, heating, to form a precursor reactive stream; introducingsaid precursor reactive stream into said reaction chamber and causingpollutant-abating reaction in said chamber.
 2. A process according toclaim 1 further comprising the steps of expelling gases from saidreaction chamber through a liquid vortex.
 3. A process according toclaim 1 , wherein said additional gas comprises hydrogen.
 4. A processaccording to claim 1 , wherein said additional gas comprises ammonia. 5.A process according to claim 1 , wherein said additional gas comprisesair.
 6. A process according to claim 1 , wherein said additional gascomprises oxygen.
 7. A process according to claim 3 , wherein saidadditional gas comprises ammonia and oxygen.
 8. A process according toclaim 3 , wherein said additional gas comprises ammonia and air.
 9. Aprocess according to claim 1 , wherein said additional gas compriseswater vapor.
 10. A process according to claim 1 , wherein saidadditional gas comprises an alcohol.
 11. A process according to claim 10, wherein said additional gas comprises methanol.
 12. A processaccording to claim 1 , wherein said additional gas comprises an ether.13. A process according to claim 12 , wherein said ether comprisesdimethyl ether.
 14. A process according to claim 1 , wherein saidadditional gas comprises an amine.
 15. A process according to claims 1,4, 5, 6 or 9 wherein said additional gas further comprises a hydrocarbon16. A process according to claim 14 , wherein said amine comprisesmethylamine.
 17. A process according to claim 1 wherein Nox is apollutant abated in said stream.
 18. A process according to any ofclaims 1 through 17, wherein said reaction of said gas stream with saidadditional gas is within a temperature range of about 650 C.-950 C. 19.A thermal reactor comprising a central chamber, heating elements, anentry end and an exit end of said chamber, a hot zone within saidcentral chamber located adjacent to said entry end wherein gasesentering said chamber at the said entry end additionally react and mixand an orifice in said central chamber for introducing air into saidcentral chamber; said orifice located upstream of said hot zone.
 20. Athermal reactor comprising a central chamber, heating elements, an entryend and an exit end of said chamber, a hot zone within said centralchamber located adjacent to said entry end wherein gases entering saidchamber at the said entry end additionally react and mix and an orificein said central chamber for introducing air into said central chamber;said orifice located downstream of said hot zone.
 21. An apparatusaccording to claim 19 or 20 , wherein said heating elements areannularly located around said chamber.
 22. An apparatus according toclaim 19 or 20 , wherein said heating elements are located within saidchamber.
 23. An apparatus for treatment of gaseous pollutants in a gasstream, said apparatus comprising: a thermal reactor comprising acentral chamber, heating elements, an entry end and an exit end of saidchamber, a side inlet communicating with an exterior air space definedby an exterior wall and said heating elements, an orifice forintroducing air to said central chamber; at least one inlet forconducting said gas stream into said reactor, said inlet comprising aconduit terminating with a portion of said conduit within said reactorwherein said portion of said conduit is located within a tube whichprojects beyond the end of said conduit to define a chamber within saidtube, said tube having an open end communicating with the interior ofsaid reactor; ports located at the entry end of said reactor chamber forintroducing a reagent into said reaction chamber directed along thewalls of said chamber to alleviate particle build up; said conduitfurther accommodating a secondary inlet for introducing other reagentinto said conduit; and a gas distributor for introducing a gas into saidcentral chamber down-stream from said open end of said tube.
 24. Anapparatus according to claim 23 , wherein said gas distributor comprisesa manifold.
 25. An apparatus according to claim 24 , wherein said gasdistributor comprises an injector.
 26. An apparatus according to claim23 , wherein said gas distributor is located out of a hot zone creatednear the open end of said tube.
 27. An apparatus according to claim 23 ,wherein said heating elements are annularly located around said chamber.28. An apparatus according to claim 23 , wherein said heating elementsare located within said chamber.